Switched-mode power supplies such as buck or buck-boost converters operate based on the cyclic charge and discharge of an inductor. The control of the charge and discharge phase often relies on a pair of power switches, a high-side power switch being used for charging the inductor and a low-side power switch being used for discharging it. Such systems rely on a careful timing operation of the switches; when one power switch is open the other is closed and vice versa. To avoid the occurrence of potential short circuits, a delay, also referred to as dead-time, may be introduced between the switching of the high-side power switch and the switching of the low-side power switch.
To minimize power losses and improve signal noise, switched-mode power supplies may be operated in a so-called resonant mode also referred to as zero-voltage mode. Operating the converter in resonant mode requires careful determination of the time at which the conductive state of the switches should be changed. This may be achieved by measuring the drain to source voltage of the low-side power switch corresponding to the voltage at the switching node. This requires a resistive voltage divider, or an auxiliary winding coupled with the primary winding of the converter. The measured voltage at the switching node is then used to detect the minimum drain voltage. The information is then processed with control logic to determine at what time to operate the power switches.
Such systems require external components which increase the cost and complexity of the device and limit its power efficiency.